007
FXUS02 KWBC 221856
PMDEPD

Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
256 PM EDT Sat Jun 22 2024

Valid 12Z Tue Jun 25 2024 - 12Z Sat Jun 29 2024

...Hazardous heat possible for southern/central portions of the
Plains and Mississippi Valley to Southeast for parts of next
week...


...Overview...

An upper level ridge will remain anchored over southwestern to
south-central parts of the nation through the week, leading to
multiple days of above normal to possibly hazardous heat. To the
north, one shortwave through the northern tier will amplify
somewhat as it crosses the Midwest/East mid- to late week. The
next system reaches the West Coast around Thursday should push a
defined surface low pressure system into the northern Plains by
late week.


...Guidance/Predictability Assessment...

The latest suite of guidance continues to offer overall good
agreement on the large scale, and typical uncertainty in the
mesoscale features that could have impacts on sensible weather/QPF
details. The first shortwave skirting the Northern Plains/Great
Lakes Tuesday-Wednesday and amplifying in the Northeast Thursday
shows better agreement in recent model guidance. Out West, models
are also converging better on timing for the upper low/trough
entering the Northwest late Wednesday and tracking east. The main
remaining outlier was the faster 00Z GFS, but the 06Z and 12Z GFS
runs seemed more reasonable. This agreement seems to hold until
around Saturday when the 00Z CMC stalls and amplifies the trough a
bit more.

The WPC forecast utilized a blend of the 06Z GFS and 00Z
ECMWF/CMC/UKMET early in the period, gradually ramping up the
proportion of GEFS and EC ensemble means as the period progressed
to help temper some of the smaller scale uncertainties. Overall,
this approach maintained fairly good continuity with the previous
WPC forecast.


...Weather/Hazards Highlights...

A low pressure system moving through south-central to eastern
Canada and its associated fronts will provide a focus for possibly
impactful convective rainfall. On Tuesday-Wednesday, copious
moisture and instability in a typical summertime convective pattern
south and east of the cold front should support widespread showers
and thunderstorms progressing eastward with the boundary from the
Mississippi Valley/Midwest into the East. As a result, large
Marginal Risks are highlighted on the Days 4 and 5 ERO to cover
this favorable environment. It is still too early to pin down any
potential areas of higher risk and the front should be fairly
progressive as well, limiting the overall threat.

Anomalous moisture and sufficient instability should persist over
the Four Corners states, eventually expanding into the southern
Rockies and parts of the High Plains much of the period and
potentially lead to some locally heavy rainfall, which could cause
flooding impacts particularly over burn scars. Marginal Risks are
in the outlook for Day 4/Tuesday across parts of Arizona and New
Mexico, expanded west a bit toward the most anomalous moisture and
east a bit to cover the Sacramento Mountains that are very
sensitive to additional rainfall. By Day 5/Wednesday, moisture
looks to be transported even farther north ahead of approaching
upper troughing, and thus the Marginal is expanded into portions of
Utah and Colorado and into the south-central High Plains. Though
perhaps not everywhere in the Marginal will see heavy rain, slow-
moving convection is a concern for these areas and warrants a
Marginal Risk. As the northwestern to north-central U.S. upper
trough and the low pressure/frontal system tracks eastward with it,
the moisture combining with these systems is likely to produce
rain/thunderstorms across the north-central U.S. again late week.
Elsewhere, parts of the Southeast/Florida may also see episodes of
diurnally enhanced convection, but overall dry conditions/high FFGs
precluded any excessive rainfall risk areas at this time.

Into Tuesday, above normal temperatures will stretch from the West
to the East, though the focus for hazardous heat will be across
the south-central Plains/Mississippi Valley into the Southeast
where daytime highs 10-15F above normal, heat/humidity could lead
to heat indices near 110F for some, and widespread major to extreme
HeatRisk are present Tuesday-Wednesday. Hazardous heat is also
possible across the Southwest where temperatures 105-115F are
likely. Temperatures should moderate back towards normal for the
East and West states as upper troughing moves through both regions
mid to late week, but upper ridging in between should bring a
return to above normal temperatures from the south-central Plains
into the Ohio and Tennessee Valleys Friday-Saturday.


Tate/Santorelli


Additional 3-7 Day Hazard information can be found on the WPC medium
range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation forecast (QPF), excessive rainfall
outlook (ERO), winter weather outlook (WWO) probabilities, heat
indices, and Key Messages can be accessed from:

https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif
https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html
https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml
https://www.wpc.ncep.noaa.gov/#page=ero
https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4
https://www.wpc.ncep.noaa.gov/heat_index.shtml
https://www.wpc.ncep.noaa.gov/#page=ovw






$$